Along with his parents, in April 1912 Widener boarded the Titanic at Cherbourg, France bound for New York City. As the ship sank Widener's mother and her maid were rescued, but Widener, his father, and his father's valet perished. In 1915, Widener's mother donated the Harry Elkins Widener Memorial Library to Harvard in his memory. Two buildings at Hill School are also dedicated to Widener, and stained glass windows at St. Paul's Episcopal Church, Elkins Park, Pennsylvania are dedicated to Widener and his father.

A Harvard legend holds that in order to spare others her son's fate, Widener's mother insisted (as a condition of her gift) that future Harvard graduates be required to learn to swim. However, while Harvard indeed implemented a swimming test in the 1920s (later dropped), this had nothing to do with Widener.[2]

As book collector

the excellence of his technical knowl­edge... His enthusiasm as a collector and his winning person­ali­ty... afforded many opportunities of obtaining treasures whose acquisition cannot be explained alone on the basis of the wealth which he commanded. Had he not perished in the Titanic catastrophe, beyond question... his library would surely have eventually become one of the greatest collec­tions of books in modern times. [He] was not satisfied alone in having a rare book or a rare book inscribed by the author; it was with him a prerequisite that the volume should be in immaculate condition.[5]